1. Technical Field
The present invention related to a sheet manufacturing apparatus.
2. Related Art
In used paper discharged from offices, used paper describing confidential matters is included. Therefore, also from the viewpoint of security protection, it is desired that such used paper can be processed in their offices. In small offices, a wet-type sheet manufacturing apparatus, which uses a large amount of water, cannot be suitably used, and therefore a dry-type sheet manufacturing apparatus simplified in structure and minimized in water usage has been proposed (see, for example, Japanese Unexamined Laid-open Patent Application Publication No. 2012-144819).
In such a sheet manufacturing apparatus, when defibrating used paper, the paper is separated into fibers and foreign substances (e.g., tonner or additive agent) other than fibers. Thereafter, at a classifying portion, a deinking process for removing foreign substances is performed. Then, using the defibrated fibers in which foreign substances were removed, a sheet is produced. There, however, arises a problem that even if performing a deinking process in the same manner, when a sheet is formed, spots, etc., by foreign substances will be generated, deteriorating the quality of the sheet. There also exists a problem that although spots, etc., by foreign substances will not be generated, the sheet thickness becomes insufficient. The problems will occur not only in cases where used paper is used as a stock material but also in cases where a pulp sheet is used as a stock material.
With respect to this, the inventors of this application have reached the conclusion that the cause is due to the difference of contents of foreign substances contained in a stock material. If the content of foreign substances in a stock material is large, the deinking process becomes insufficient, which results in a mixture of foreign substances in the collected (classified) defibrated fibers. Further, if the content of foreign substances in a stock material is small, defibrated fibers will be removed together with foreign substances by a deinking process, deteriorating the collection rate of defibrated fibers, which in turn results in an insufficient thickness when forming into a sheet. However, no device for easily measuring the content of foreign substances contained in a stock material has been available. Further, there was no disclosure on how to control depending on the content of foreign substances.